Method and device for transmitting and receiving list of cells providing SCPTM service

ABSTRACT

Provided is a method for a MCE transmitting a list of cells providing a SCPTM service in a wireless communication system. A MCE may receive a cell ID list from a MME and transmit the cell ID list received from the MME to a base station. The cell ID list transmitted to the base station and the cell ID list received from the MME may be identical. Provided is a method for a base station receiving a list of cells providing a SCPTM service in a wireless communication system. A base station may receive, from a MCE, a cell ID list received from a MME, and on the basis of the cell ID list received from the MCE, perform a SCPTM service. The cell ID list received from the MCE and the cell ID list received from the MME may be identical.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is continuation of U.S. patent application Ser. No.15/558,174, filed on Sep. 13, 2017, now U.S. Pat. No. 10,231,174, whichis the National Stage filing under 35 U.S.C. 371 of InternationalApplication No. PCT/KR2016/002541, filed on Mar. 15, 2016, which claimsthe benefit of U.S. Provisional Application No. 62/134,011, filed onMar. 17, 2015 and 62/204,467, filed on Aug. 13, 2015, the contents ofwhich are all hereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless communication system, andmore particularly, to a method in which a multi-cell coordination entity(MCE) receives a list of cells for providing a single-cellpoint-to-multipoint (SCPTM) service from a mobility management entity(MME) and provides it to a base station, and a device supporting themethod.

Related Art

3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) thatis an advancement of UMTS (Universal Mobile Telecommunication System) isbeing introduced with 3GPP release 8. In 3GPP LTE, OFDMA (orthogonalfrequency division multiple access) is used for downlink, and SC-FDMA(single carrier-frequency division multiple access) is used for uplink.The 3GPP LTE adopts MIMO (multiple input multiple output) having maximumfour antennas. Recently, a discussion of 3GPP LTE-A (LTE-Advanced) whichis the evolution of the 3GPP LTE is in progress.

A Multimedia Broadcast/Multicast Service (MBMS) is a service ofsimultaneously transmitting a data packet to a plurality of users,similar to an existing Cell Broadcast Service (CBS). However, the CBS isa low-speed message-based service, while the MBMS is designed forhigh-speed multimedia data transmission. Further, the CBS is notInternet Protocol (IP)-based, whereas the MBMS is based on IP multicast.According to the MBMS, when users of a certain level are present in thesame cell, the users are allowed to receive the same multimedia datausing a shared resource (or channel), and thus the efficiency of radioresources may be improved and the users may use a multimedia service atlow costs.

The MBMS uses a shared channel so that a plurality of UEs efficientlyreceives data on one service. A BS allocates only one shared channel fordata on one service, instead of allocating as many dedicated channels asthe number of UEs to receive the service in one cell. The plurality ofUEs simultaneously receives the shared channel, thus improving theefficiency of radio resources. Regarding the MBMS, a UE may receive theMBMS after receiving system information on the cell.

An important communication technique such as public safety or groupcommunication system enablers for LTE (GCSE_LTE) has been introduced inRel-12. In Rel-12 GCSE, group communication has been designated aseMBMS. The eMBMS is designed to supply media content to a pre-plannedwide area (i.e., an MBSFN area). The MBSFN area is rather static (e.g.,configured by O&M), and cannot be dynamically adjusted according to userdistribution. Even if all radio resources of a frequency domain is notused, eMBMS transmission may occupy a full system bandwidth, andmultiplexing with unicast is not allowed in the same subframe. An MBSFNsubframe configuration is also rather static (e.g., configured by O&M).That is, an MBSFN subframe cannot be dynamically adjusted according tothe number of dynamic groups and a traffic load of a dynamic group.Therefore, when providing an importance communication service, a radioresource configuration for the eMBMS may be unnecessarily wasted.Therefore, single-cell point-to-multipoint (SCPTM) transmission isproposed for an effective use of the radio resource. While identifiablesignals are transmitted simultaneously in a plurality of cells in theMBSFN transmission, the MBMS service is transmitted in a single cell inthe SCPTM transmission.

SUMMARY OF THE INVENTION

A single-cell point-to-multipoint (SCPTM) service is broadcast, but istransmitted through a dedicated traffic channel (DTCH). Thus, the SCTPMservice may have a problem in continuous reception when a terminal movesto a cell of a neighboring base station which does not provide the sameSCPTM service. Accordingly, a serving base station needs to know SCPTMservice information of the neighboring base station. Therefore, thepresent invention proposes a method of transmitting or receiving a listof cells for providing the SCPTM service and a device supporting themethod.

According to one embodiment, it is provided a method in which amulti-cell coordination entity (MCE) transmits a list of cells forproviding an SCPTM service in a wireless communication system. The MCEmay receive a cell identification (ID) list from a mobility managemententity (MME), and may transmit to a base station the cell ID receivedfrom the MME. The cell ID list transmitted to the base station may beidentical to the cell ID list received from the MME.

The cell ID list received from the MME may include a list of cells forproviding the SCPTM service. The cell for providing the SCPTM servicemay be a cell for providing the SCPTM service among cells managed by theMME. The cell ID list received from the MME may be received by beingincluded in any one of a multimedia broadcast/multicast service (MBMS)session update request message and an MBSM session stop request message.The cell ID list transmitted to the base station may be transmitted bybeing included in any one of an MBSM session start request message, anMBSM session update request message, and an MBMS session stop requestmessage.

Further, the MCE may receive an MBMS session response message, an MBMSsession update response message, and an MBMS session stop responsemessage.

According to another embodiment, it is provided a method in which a basestation receives a list of cells for providing an SCPTM service in awireless communication system. The base station may receive from an MCEa cell ID list received from an MME, and may perform the SCPTM serviceon the basis of the cell ID list received from the MCE. The cell ID listreceived from the MCE may be identical to the cell ID list received fromthe MME.

The cell ID list received from the MME may include a list of cells forproviding the SCPTM service. The cell for providing the SCPTM servicemay be a cell for providing the SCPTM service among cells managed by theMME.

The cell ID list received from the MCE may be received by being includedin an MBMS session start request message or an MBMS session updaterequest message. Further, the base station may store the cell ID listreceived from the MCE.

The cell ID list received from the MCE may be received by being includedin an MBMS session stop request message. Further, the base station mayremove the cell ID list received from the MCE.

According to another embodiment, it is provided a base station forreceiving a list of cells for providing an SCPTM service in a wirelesscommunication system. The base station includes: a memory; atransceiver, and a processor operatively coupled to the memory and thetransceiver. The processor may be configured for: controlling thetransceiver to receive from an MCE a cell ID list received from an MME;and performing the SCPTM service on the basis of the cell ID listreceived from the MCE. The cell ID list received from the MCE may beidentical to the cell ID list received from the MME.

The cell ID list received from the MME may include a list of cells forproviding the SCPTM service.

Continuity of single-cell point-to-multipoint (SCPTM) service receptioncan be supported by receiving information regarding an SCPTM servicefrom a neighboring base station.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows LTE system architecture.

FIG. 2 shows a network architecture for an MBMS.

FIG. 3 shows a control plane and a user plane of a radio interfaceprotocol of an LTE system.

FIG. 4 shows a procedure in which UE that is initially powered onexperiences a cell selection process, registers it with a network, andthen performs cell reselection if necessary.

FIG. 5 shows an RRC connection establishment procedure.

FIG. 6 shows an RRC connection reconfiguration procedure.

FIG. 7 shows an RRC connection re-establishment procedure.

FIG. 8 shows a structure of an MBSFN subframe.

FIG. 9 shows an example of an MBSFN subframe configuration forperforming an MBMS service.

FIG. 10 shows a problem for supporting service continuity.

FIG. 11 shows a method in which an eNB supporting an SCPTM serviceprovides identification information to a neighboring eNB according to anembodiment of the present invention.

FIG. 12 shows a method in which an eNB supporting an SCPTM serviceprovides identification information to a neighboring eNB according to anembodiment of the present invention.

FIG. 13 shows a method in which an MCE provides a cell ID list to an eNBaccording to an embodiment of the present invention.

FIG. 14 is a block diagram illustrating a method in which an MCEtransmits a list of cells for providing an SCPTM service according to anembodiment of the present invention.

FIG. 15 is a block diagram illustrating a method in which an eNBreceives a list or cells for providing an SCPTM service according to anembodiment of the present invention.

FIG. 16 is a block diagram illustrating a wireless communication systemaccording to the embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is evolved from IEEE 802.16e, and provides backwardcompatibility with a system based on the IEEE 802.16e. The UTRA is apart of a universal mobile telecommunication system (UMTS). 3rdgeneration partnership project (3GPP) long term evolution (LTE) is apart of an evolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses theOFDMA in a downlink and uses the SC-FDMA in an uplink. LTE-advanced(LTE-A) is an evolution of the LTE.

For clarity, the following description will focus on LTE-A. However,technical features of the present invention are not limited thereto.

FIG. 1 shows LTE system architecture. The communication network iswidely deployed to provide a variety of communication services such asvoice over internet protocol (VoIP) through IMS and packet data.

Referring to FIG. 1, the LTE system architecture includes one or moreuser equipment (UE; 10), an evolved-UMTS terrestrial radio accessnetwork (E-UTRAN) and an evolved packet core (EPC). The UE 10 refers toa communication equipment carried by a user. The UE 10 may be fixed ormobile, and may be referred to as another terminology, such as a mobilestation (MS), a user terminal (UT), a subscriber station (SS), awireless device, etc.

The E-UTRAN includes one or more evolved node-B (eNB) 20, and aplurality of UEs may be located in one cell. The eNB 20 provides an endpoint of a control plane and a user plane to the UE 10. The eNB 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as a base station (BS), a basetransceiver system (BTS), an access point, etc. One eNB 20 may bedeployed per cell. There are one or more cells within the coverage ofthe eNB 20. A single cell is configured to have one of bandwidthsselected from 1.25, 2.5, 5, 10, and 20 MHz, etc., and provides downlinkor uplink transmission services to several UEs. In this case, differentcells can be configured to provide different bandwidths.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 tothe UE 10, and an uplink (UL) denotes communication from the UE 10 tothe eNB 20. In the DL, a transmitter may be a part of the eNB 20, and areceiver may be a part of the UE 10. In the UL, the transmitter may be apart of the UE 10, and the receiver may be a part of the eNB 20.

The EPC includes a mobility management entity (MME) which is in chargeof control plane functions, and a system architecture evolution (SAE)gateway (S-GW) which is in charge of user plane functions. The MME/S-GW30 may be positioned at the end of the network and connected to anexternal network. The MME has UE access information or UE capabilityinformation, and such information may be primarily used in UE mobilitymanagement. The S-GW is a gateway of which an endpoint is an E-UTRAN.The MME/S-GW 30 provides an end point of a session and mobilitymanagement function for the UE 10. The EPC may further include a packetdata network (PDN) gateway (PDN-GW). The PDN-GW is a gateway of which anendpoint is a PDN.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, Inter core network (CN) node signaling for mobilitybetween 3GPP access networks, idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), P-GW and S-GW selection,MME selection for handovers with MME change, serving GPRS support node(SGSN) selection for handovers to 2G or 3G 3GPP access networks,roaming, authentication, bearer management functions including dedicatedbearer establishment, support for public warning system (PWS) (whichincludes earthquake and tsunami warning system (ETWS) and commercialmobile alert system (CMAS)) message transmission. The S-GW host providesassorted functions including per-user based packet filtering (by e.g.,deep packet inspection), lawful interception, UE Internet protocol (IP)address allocation, transport level packet marking in the DL, UL and DLservice level charging, gating and rate enforcement, DL rate enforcementbased on APN-AMBR. For clarity MME/S-GW 30 will be referred to hereinsimply as a “gateway,” but it is understood that this entity includesboth the MME and S-GW.

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 and the eNB 20 are connected by means of a Uu interface. TheeNBs 20 are interconnected by means of an X2 interface. Neighboring eNBsmay have a meshed network structure that has the X2 interface. The eNBs20 are connected to the EPC by means of an S1 interface. The eNBs 20 areconnected to the MME by means of an S1-MME interface, and are connectedto the S-GW by means of S1-U interface. The S1 interface supports amany-to-many relation between the eNB 20 and the MME/S-GW.

The eNB 20 may perform functions of selection for gateway 30, routingtoward the gateway 30 during a radio resource control (RRC) activation,scheduling and transmitting of paging messages, scheduling andtransmitting of broadcast channel (BCH) information, dynamic allocationof resources to the UEs 10 in both UL and DL, configuration andprovisioning of eNB measurements, radio bearer control, radio admissioncontrol (RAC), and connection mobility control in LTE_ACTIVE state. Inthe EPC, and as noted above, gateway 30 may perform functions of pagingorigination, LTE_IDLE state management, ciphering of the user plane, SAEbearer control, and ciphering and integrity protection of NAS signaling.

FIG. 2 shows a network architecture for a Multimedia Broadcast/MulticastService (MBMS).

Referring to FIG. 2, the radio access network (EUTRAN, 200) includes amulti-cell coordination entity (hereinafter, “MCE”, 210) and a basestation (eNB, 220). The MCE 210 is a main entity for controlling theMBMS and plays a role to perform session management, radio resourceallocation or admission control of the base station 220. The MCE 210 maybe implemented in the base station 220 or may be implemented independentfrom the base station 220. The interface between the MCE 210 and thebase station 220 is called M2 interface. The M2 interface is an internalcontrol plane interface of the radio access network 200 and MBMS controlinformation is transmitted through the M2 interface. In case the MCE 210is implemented in the base station 220, the M2 interface may be presentonly logically.

The EPC (Evolved Packet Core, 250) includes an MME 260 and an MBMSgateway (GW) 270. The MBMS gateway 270 is an entity for transmittingMBMS service data and is positioned between the base station 220 and theBM-SC and performs MBMS packet transmission and broadcast to the basestation 220. The MBMS gateway 270 uses a PDCP and IP multicast totransmit user data to the base station 220 and performs session controlsignaling for the radio access network 200.

The interface between the MME 260 and the MCE 210 is a control planeinterface between the radio access network 200 and the EPC 250 and iscalled M3 interface. Control information related to MBMS session controlis transmitted through the M3 interface. The MME 260 and the MCE 210transmits, to the base station 220, session control signaling such as asession start/stop message for session start or session stop, and thebase station 220 may inform the UE through a cell notification that thecorresponding MBMS service has been started or stopped.

The interface between the base station 220 and the MBMS gateway 270 is auser plane interface and is called M1 interface.

FIG. 3 shows a control plane and a user plane of a radio interfaceprotocol of an LTE system. FIG. 3(a) shows a control plane of a radiointerface protocol of an LTE system. FIG. 3(b) shows a user plane of aradio interface protocol of an LTE system.

Layers of a radio interface protocol between the UE and the E-UTRAN maybe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. The radio interface protocol between the UE and the E-UTRAN maybe horizontally divided into a physical layer, a data link layer, and anetwork layer, and may be vertically divided into a control plane(C-plane) which is a protocol stack for control signal transmission anda user plane (U-plane) which is a protocol stack for data informationtransmission. The layers of the radio interface protocol exist in pairsat the UE and the E-UTRAN, and are in charge of data transmission of theUu interface.

A physical (PHY) layer belongs to the L1. The PHY layer provides ahigher layer with an information transfer service through a physicalchannel. The PHY layer is connected to a medium access control (MAC)layer, which is a higher layer of the PHY layer, through a transportchannel. A physical channel is mapped to the transport channel. Data istransferred between the MAC layer and the PHY layer through thetransport channel. Between different PHY layers, i.e., a PHY layer of atransmitter and a PHY layer of a receiver, data is transferred throughthe physical channel using radio resources. The physical channel ismodulated using an orthogonal frequency division multiplexing (OFDM)scheme, and utilizes time and frequency as a radio resource.

The PHY layer uses several physical control channels. A physicaldownlink control channel (PDCCH) reports to a UE about resourceallocation of a paging channel (PCH) and a downlink shared channel(DL-SCH), and hybrid automatic repeat request (HARQ) information relatedto the DL-SCH. The PDCCH may carry a UL grant for reporting to the UEabout resource allocation of UL transmission. A physical control formatindicator channel (PCFICH) reports the number of OFDM symbols used forPDCCHs to the UE, and is transmitted in every subframe. A physicalhybrid ARQ indicator channel (PHICH) carries an HARQ acknowledgement(ACK)/non-acknowledgement (NACK) signal in response to UL transmission.A physical uplink control channel (PUCCH) carries UL control informationsuch as HARQ ACK/NACK for DL transmission, scheduling request, and CQI.A physical uplink shared channel (PUSCH) carries a UL-uplink sharedchannel (SCH).

A physical channel consists of a plurality of subframes in time domainand a plurality of subcarriers in frequency domain. One subframeconsists of a plurality of symbols in the time domain. One subframeconsists of a plurality of resource blocks (RBs). One RB consists of aplurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use specific subcarriers of specific symbols of acorresponding subframe for a PDCCH. For example, a first symbol of thesubframe may be used for the PDCCH. The PDCCH carries dynamic allocatedresources, such as a physical resource block (PRB) and modulation andcoding scheme (MCS). A transmission time interval (TTI) which is a unittime for data transmission may be equal to a length of one subframe. Thelength of one subframe may be 1 ms.

The transport channel is classified into a common transport channel anda dedicated transport channel according to whether the channel is sharedor not. A DL transport channel for transmitting data from the network tothe UE includes a broadcast channel (BCH) for transmitting systeminformation, a paging channel (PCH) for transmitting a paging message, aDL-SCH for transmitting user traffic or control signals, etc. The DL-SCHsupports HARQ, dynamic link adaptation by varying the modulation, codingand transmit power, and both dynamic and semi-static resourceallocation. The DL-SCH also may enable broadcast in the entire cell andthe use of beamforming. The system information carries one or moresystem information blocks. All system information blocks may betransmitted with the same periodicity. Traffic or control signals of amultimedia broadcast/multicast service (MBMS) may be transmitted throughthe DL-SCH or a multicast channel (MCH).

A UL transport channel for transmitting data from the UE to the networkincludes a random access channel (RACH) for transmitting an initialcontrol message, a UL-SCH for transmitting user traffic or controlsignals, etc. The UL-SCH supports HARQ and dynamic link adaptation byvarying the transmit power and potentially modulation and coding. TheUL-SCH also may enable the use of beamforming. The RACH is normally usedfor initial access to a cell.

A MAC layer belongs to the L2. The MAC layer provides services to aradio link control (RLC) layer, which is a higher layer of the MAClayer, via a logical channel. The MAC layer provides a function ofmapping multiple logical channels to multiple transport channels. TheMAC layer also provides a function of logical channel multiplexing bymapping multiple logical channels to a single transport channel A MACsublayer provides data transfer services on logical channels.

The logical channels are classified into control channels fortransferring control plane information and traffic channels fortransferring user plane information, according to a type of transmittedinformation. That is, a set of logical channel types is defined fordifferent data transfer services offered by the MAC layer. The logicalchannels are located above the transport channel, and are mapped to thetransport channels.

The control channels are used for transfer of control plane informationonly. The control channels provided by the MAC layer include a broadcastcontrol channel (BCCH), a paging control channel (PCCH), a commoncontrol channel (CCCH), a multicast control channel (MCCH) and adedicated control channel (DCCH). The BCCH is a downlink channel forbroadcasting system control information. The PCCH is a downlink channelthat transfers paging information and is used when the network does notknow the location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting MBMS control information from the networkto a UE. The DCCH is a point-to-point bi-directional channel used by UEshaving an RRC connection that transmits dedicated control informationbetween a UE and the network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by the MAC layer include a dedicatedtraffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCHis a point-to-point channel, dedicated to one UE for the transfer ofuser information and can exist in both uplink and downlink. The MTCH isa point-to-multipoint downlink channel for transmitting traffic datafrom the network to the UE.

Uplink connections between logical channels and transport channelsinclude the DCCH that can be mapped to the UL-SCH, the DTCH that can bemapped to the UL-SCH and the CCCH that can be mapped to the UL-SCH.Downlink connections between logical channels and transport channelsinclude the BCCH that can be mapped to the BCH or DL-SCH, the PCCH thatcan be mapped to the PCH, the DCCH that can be mapped to the DL-SCH, andthe DTCH that can be mapped to the DL-SCH, the MCCH that can be mappedto the MCH, and the MTCH that can be mapped to the MCH.

An RLC layer belongs to the L2. The RLC layer provides a function ofadjusting a size of data, so as to be suitable for a lower layer totransmit the data, by concatenating and segmenting the data receivedfrom an upper layer in a radio section. In addition, to ensure a varietyof quality of service (QoS) required by a radio bearer (RB), the RLClayer provides three operation modes, i.e., a transparent mode (TM), anunacknowledged mode (UM), and an acknowledged mode (AM). The AM RLCprovides a retransmission function through an automatic repeat request(ARQ) for reliable data transmission. Meanwhile, a function of the RLClayer may be implemented with a functional block inside the MAC layer.In this case, the RLC layer may not exist.

A packet data convergence protocol (PDCP) layer belongs to the L2. ThePDCP layer provides a function of header compression function thatreduces unnecessary control information such that data being transmittedby employing IP packets, such as IPv4 or IPv6, can be efficientlytransmitted over a radio interface that has a relatively smallbandwidth. The header compression increases transmission efficiency inthe radio section by transmitting only necessary information in a headerof the data. In addition, the PDCP layer provides a function ofsecurity. The function of security includes ciphering which preventsinspection of third parties, and integrity protection which preventsdata manipulation of third parties.

A radio resource control (RRC) layer belongs to the L3. The RLC layer islocated at the lowest portion of the L3, and is only defined in thecontrol plane. The RRC layer takes a role of controlling a radioresource between the UE and the network. For this, the UE and thenetwork exchange an RRC message through the RRC layer. The RRC layercontrols logical channels, transport channels, and physical channels inrelation to the configuration, reconfiguration, and release of RBs. AnRB is a logical path provided by the L1 and L2 for data delivery betweenthe UE and the network. That is, the RB signifies a service provided theL2 for data transmission between the UE and E-UTRAN. The configurationof the RB implies a process for specifying a radio protocol layer andchannel properties to provide a particular service and for determiningrespective detailed parameters and operations. The RB is classified intotwo types, i.e., a signaling RB (SRB) and a data RB (DRB). The SRB isused as a path for transmitting an RRC message in the control plane. TheDRB is used as a path for transmitting user data in the user plane.

A Non-Access Stratum (NAS) layer placed over the RRC layer performsfunctions, such as session management and mobility management.

Referring to FIG. 3(a), the RLC and MAC layers (terminated in the eNB onthe network side) may perform functions such as scheduling, automaticrepeat request (ARQ), and hybrid automatic repeat request (HARQ). TheRRC layer (terminated in the eNB on the network side) may performfunctions such as broadcasting, paging, RRC connection management, RBcontrol, mobility functions, and UE measurement reporting andcontrolling. The NAS control protocol (terminated in the MME of gatewayon the network side) may perform functions such as a SAE bearermanagement, authentication, LTE_IDLE mobility handling, pagingorigination in LTE_IDLE, and security control for the signaling betweenthe gateway and UE.

Referring to FIG. 3(b), the RLC and MAC layers (terminated in the eNB onthe network side) may perform the same functions for the control plane.The PDCP layer (terminated in the eNB on the network side) may performthe user plane functions such as header compression, integrityprotection, and ciphering.

Hereinafter, An RRC state of a UE and RRC connection procedure aredescribed.

An RRC state indicates whether an RRC layer of the UE is logicallyconnected to an RRC layer of the E-UTRAN. The RRC state may be dividedinto two different states such as an RRC connected state and an RRC idlestate. When an RRC connection is established between the RRC layer ofthe UE and the RRC layer of the E-UTRAN, the UE is in RRC_CONNECTED, andotherwise the UE is in RRC_IDLE. Since the UE in RRC_CONNECTED has theRRC connection established with the E-UTRAN, the E-UTRAN may recognizethe existence of the UE in RRC_CONNECTED and may effectively control theUE. Meanwhile, the UE in RRC_IDLE may not be recognized by the E-UTRAN,and a CN manages the UE in unit of a TA which is a larger area than acell. That is, only the existence of the UE in RRC_IDLE is recognized inunit of a large area, and the UE must transition to RRC_CONNECTED toreceive a typical mobile communication service such as voice or datacommunication.

In RRC_IDLE state, the UE may receive broadcasts of system informationand paging information while the UE specifies a discontinuous reception(DRX) configured by NAS, and the UE has been allocated an identification(ID) which uniquely identifies the UE in a tracking area and may performpublic land mobile network (PLMN) selection and cell reselection. Also,in RRC_IDLE state, no RRC context is stored in the eNB.

In RRC_CONNECTED state, the UE has an E-UTRAN RRC connection and acontext in the E-UTRAN, such that transmitting and/or receiving datato/from the eNB becomes possible. Also, the UE can report channelquality information and feedback information to the eNB. InRRC_CONNECTED state, the E-UTRAN knows the cell to which the UE belongs.Therefore, the network can transmit and/or receive data to/from UE, thenetwork can control mobility (handover and inter-radio accesstechnologies (RAT) cell change order to GSM EDGE radio access network(GERAN) with network assisted cell change (NACC)) of the UE, and thenetwork can perform cell measurements for a neighboring cell.

In RRC_IDLE state, the UE specifies the paging DRX cycle. Specifically,the UE monitors a paging signal at a specific paging occasion of everyUE specific paging DRX cycle. The paging occasion is a time intervalduring which a paging signal is transmitted. The UE has its own pagingoccasion.

A paging message is transmitted over all cells belonging to the sametracking area. If the UE moves from one TA to another TA, the UE willsend a tracking area update (TAU) message to the network to update itslocation.

When the user initially powers on the UE, the UE first searches for aproper cell and then remains in RRC_IDLE in the cell. When there is aneed to establish an RRC connection, the UE which remains in RRC_IDLEestablishes the RRC connection with the RRC of the E-UTRAN through anRRC connection procedure and then may transition to RRC_CONNECTED. TheUE which remains in RRC_IDLE may need to establish the RRC connectionwith the E-UTRAN when uplink data transmission is necessary due to auser's call attempt or the like or when there is a need to transmit aresponse message upon receiving a paging message from the E-UTRAN.

To manage mobility of the UE in the NAS layer, two states are defined,i.e., an EPS mobility management-REGISTERED (EMM-REGISTERED) state andan EMM-DEREGISTERED state. These two states apply to the UE and the MME.Initially, the UE is in the EMM-DEREGISTERED state. To access a network,the UE performs a process of registering to the network through aninitial attach procedure. If the attach procedure is successfullyperformed, the UE and the MME enter the EMM-REGISTERED state.

To manage a signaling connection between the UE and the EPC, two statesare defined, i.e., an EPS connection management (ECM)-IDLE state and anECM-CONNECTED state. These two states apply to the UE and the MME. Whenthe UE in the ECM-IDLE state establishes an RRC connection with theE-UTRAN, the UE enters the ECM-CONNECTED state. When the MME in theECM-IDLE state establishes an S1 connection with the E-UTRAN, the MMEenters the ECM-CONNECTED state. When the UE is in the ECM-IDLE state,the E-UTRAN does not have context information of the UE. Therefore, theUE in the ECM-IDLE state performs a UE-based mobility related proceduresuch as cell selection or reselection without having to receive acommand of the network. On the other hand, when the UE is in theECM-CONNECTED state, mobility of the UE is managed by the command of thenetwork. If a location of the UE in the ECM-IDLE state becomes differentfrom a location known to the network, the UE reports the location of theUE to the network through a tracking area update procedure.

FIG. 4 shows a procedure in which UE that is initially powered onexperiences a cell selection process, registers it with a network, andthen performs cell reselection if necessary.

Referring to FIG. 4, the UE selects Radio Access Technology (RAT) inwhich the UE communicates with a Public Land Mobile Network (PLMN), thatis, a network from which the UE is provided with service (S410).Information about the PLMN and the RAT may be selected by the user ofthe UE, and the information stored in a Universal Subscriber IdentityModule (USIM) may be used.

The UE selects a cell that has the greatest value and that belongs tocells having measured BS and signal intensity or quality greater than aspecific value (cell selection) (S420). In this case, the UE that ispowered off performs cell selection, which may be called initial cellselection. A cell selection procedure is described later in detail.After the cell selection, the UE receives system informationperiodically by the BS. The specific value refers to a value that isdefined in a system in order for the quality of a physical signal indata transmission/reception to be guaranteed. Accordingly, the specificvalue may differ depending on applied RAT.

If network registration is necessary, the UE performs a networkregistration procedure (S430). The UE registers its information (e.g.,an IMSI) with the network in order to receive service (e.g., paging)from the network. The UE does not register it with a network whenever itselects a cell, but registers it with a network when information aboutthe network (e.g., a Tracking Area Identity (TAI)) included in systeminformation is different from information about the network that isknown to the UE.

The UE performs cell reselection based on a service environment providedby the cell or the environment of the UE (S440). If the value of theintensity or quality of a signal measured based on a BS from which theUE is provided with service is lower than that measured based on a BS ofa neighboring cell, the UE selects a cell that belongs to other cellsand that provides better signal characteristics than the cell of the BSthat is accessed by the UE. This process is called cell reselectiondifferently from the initial cell selection of the No. 2 process. Inthis case, temporal restriction conditions are placed in order for acell to be frequently reselected in response to a change of signalcharacteristic. A cell reselection procedure is described later indetail.

FIG. 5 shows an RRC connection establishment procedure.

The UE sends an RRC connection request message that requests RRCconnection to a network (S510). The network sends an RRC connectionestablishment message as a response to the RRC connection request(S520). After receiving the RRC connection establishment message, the UEenters RRC connected mode.

The UE sends an RRC connection establishment complete message used tocheck the successful completion of the RRC connection to the network(S530).

FIG. 6 shows an RRC connection reconfiguration procedure.

An RRC connection reconfiguration is used to modify RRC connection. Thisis used to establish/modify/release RBs, perform handover, and setup/modify/release measurements.

A network sends an RRC connection reconfiguration message for modifyingRRC connection to UE (S610). As a response to the RRC connectionreconfiguration message, the UE sends an RRC connection reconfigurationcomplete message used to check the successful completion of the RRCconnection reconfiguration to the network (S620).

The following is a detailed description of a procedure of selecting acell by a terminal.

When power is turned-on or the terminal is located in a cell, theterminal performs procedures for receiving a service byselecting/reselecting a suitable quality cell.

A terminal in an RRC idle state should prepare to receive a servicethrough the cell by always selecting a suitable quality cell. Forexample, a terminal where power is turned-on just before should selectthe suitable quality cell to be registered in a network. If the terminalin an RRC connection state enters in an RRC idle state, the terminalshould selects a cell for stay in the RRC idle state. In this way, aprocedure of selecting a cell satisfying a certain condition by theterminal in order to be in a service idle state such as the RRC idlestate refers to cell selection. Since the cell selection is performed ina state that a cell in the RRC idle state is not currently determined,it is important to select the cell as rapid as possible. Accordingly, ifthe cell provides a wireless signal quality of a predetermined level orgreater, although the cell does not provide the best wireless signalquality, the cell may be selected during a cell selection procedure ofthe terminal.

Hereinafter, a method and a procedure of selecting a cell by a terminalin a 3GPP LTE is described.

A cell selection process is basically divided into two types.

The first is an initial cell selection process. In this process, UE doesnot have preliminary information about a wireless channel. Accordingly,the UE searches for all wireless channels in order to find out a propercell. The UE searches for the strongest cell in each channel.Thereafter, if the UE has only to search for a suitable cell thatsatisfies a cell selection criterion, the UE selects the correspondingcell.

Next, the UE may select the cell using stored information or usinginformation broadcasted by the cell. Accordingly, cell selection may befast compared to an initial cell selection process. If the UE has onlyto search for a cell that satisfies the cell selection criterion, the UEselects the corresponding cell. If a suitable cell that satisfies thecell selection criterion is not retrieved though such a process, the UEperforms an initial cell selection process.

After the UE selects a specific cell through the cell selection process,the intensity or quality of a signal between the UE and a BS may bechanged due to a change in the mobility or wireless environment of theUE. Accordingly, if the quality of the selected cell is deteriorated,the UE may select another cell that provides better quality. If a cellis reselected as described above, the UE selects a cell that providesbetter signal quality than the currently selected cell. Such a processis called cell reselection. In general, a basic object of the cellreselection process is to select a cell that provides UE with the bestquality from a viewpoint of the quality of a radio signal.

In addition to the viewpoint of the quality of a radio signal, a networkmay determine priority corresponding to each frequency, and may informthe UE of the determined priorities. The UE that has received thepriorities preferentially takes into consideration the priorities in acell reselection process compared to a radio signal quality criterion.

As described above, there is a method of selecting or reselecting a cellaccording to the signal characteristics of a wireless environment. Inselecting a cell for reselection when a cell is reselected, thefollowing cell reselection methods may be present according to the RATand frequency characteristics of the cell.

-   -   Intra-frequency cell reselection: UE reselects a cell having the        same center frequency as that of RAT, such as a cell on which        the UE camps on.    -   Inter-frequency cell reselection: UE reselects a cell having a        different center frequency from that of RAT, such as a cell on        which the UE camps on    -   Inter-RAT cell reselection: UE reselects a cell that uses RAT        different from RAT on which the UE camps

The principle of a cell reselection process is as follows.

First, UE measures the quality of a serving cell and neighbor cells forcell reselection.

Second, cell reselection is performed based on a cell reselectioncriterion. The cell reselection criterion has the followingcharacteristics in relation to the measurements of a serving cell andneighbor cells.

Intra-frequency cell reselection is basically based on ranking. Rankingis a task for defining a criterion value for evaluating cell reselectionand numbering cells using criterion values according to the size of thecriterion values. A cell having the best criterion is commonly calledthe best-ranked cell. The cell criterion value is based on the value ofa corresponding cell measured by UE, and may be a value to which afrequency offset or cell offset has been applied, if necessary.

Inter-frequency cell reselection is based on frequency priority providedby a network. UE attempts to camp on a frequency having the highestfrequency priority. A network may provide frequency priority that willbe applied by UEs within a cell in common through broadcastingsignaling, or may provide frequency-specific priority to each UE throughUE-dedicated signaling. A cell reselection priority provided throughbroadcast signaling may refer to a common priority. A cell reselectionpriority for each terminal set by a network may refer to a dedicatedpriority. If receiving the dedicated priority, the terminal may receivea valid time associated with the dedicated priority together. Ifreceiving the dedicated priority, the terminal starts a validity timerset as the received valid time together therewith. While the valid timeris operated, the terminal applies the dedicated priority in the RRC idlemode. If the valid timer is expired, the terminal discards the dedicatedpriority and again applies the common priority.

For the inter-frequency cell reselection, a network may provide UE witha parameter (e.g., a frequency-specific offset) used in cell reselectionfor each frequency.

For the intra-frequency cell reselection or the inter-frequency cellreselection, a network may provide UE with a Neighboring Cell List (NCL)used in cell reselection. The NCL includes a cell-specific parameter(e.g., a cell-specific offset) used in cell reselection.

For the intra-frequency or inter-frequency cell reselection, a networkmay provide UE with a cell reselection black list used in cellreselection. The UE does not perform cell reselection on a cell includedin the black list.

Ranking performed in a cell reselection evaluation process is describedbelow.

A ranking criterion used to apply priority to a cell is defined as inEquation 1.R _(S) =Q _(meas,s) +Q _(hyst) , R _(n) =Q _(meas,n) −Q_(offset)  [Equation 1]

In this case, Rs is the ranking criterion of a serving cell, Rn is theranking criterion of a neighbor cell, Qmeas,s is the quality value ofthe serving cell measured by UE, Qmeas,n is the quality value of theneighbor cell measured by UE, Qhyst is the hysteresis value for ranking,and Qoffset is an offset between the two cells.

In Intra-frequency, if UE receives an offset “Qoffsets,n” between aserving cell and a neighbor cell, Qoffset=Qoffsets,n. If UE does notQoffsets,n, Qoffset=0.

In Inter-frequency, if UE receives an offset “Qoffsets,n” for acorresponding cell, Qoffset=Qoffsets,n+Qfrequency. If UE does notreceive “Qoffsets,n”, Qoffset=Qfrequency.

If the ranking criterion Rs of a serving cell and the ranking criterionRn of a neighbor cell are changed in a similar state, ranking priorityis frequency changed as a result of the change, and UE may alternatelyreselect the twos. Qhyst is a parameter that gives hysteresis to cellreselection so that UE is prevented from to alternately reselecting twocells.

UE measures RS of a serving cell and Rn of a neighbor cell according tothe above equation, considers a cell having the greatest rankingcriterion value to be the best-ranked cell, and reselects the cell. If areselected cell is not a suitable cell, UE excludes a correspondingfrequency or a corresponding cell from the subject of cell reselection.

FIG. 7 shows an RRC connection re-establishment procedure.

Referring to FIG. 7, UE stops using all the radio bearers that have beenconfigured other than a Signaling Radio Bearer (SRB) #0, and initializesa variety of kinds of sublayers of an Access Stratum (AS) (S710).Furthermore, the UE configures each sublayer and the PHY layer as adefault configuration. In this procedure, the UE maintains the RRCconnection state.

The UE performs a cell selection procedure for performing an RRCconnection reconfiguration procedure (S720). The cell selectionprocedure of the RRC connection re-establishment procedure may beperformed in the same manner as the cell selection procedure that isperformed by the UE in the RRC idle state, although the UE maintains theRRC connection state.

After performing the cell selection procedure, the UE determines whetheror not a corresponding cell is a suitable cell by checking the systeminformation of the corresponding cell (S730). If the selected cell isdetermined to be a suitable E-UTRAN cell, the UE sends an RRC connectionre-establishment request message to the corresponding cell (S740).

Meanwhile, if the selected cell is determined to be a cell that uses RATdifferent from that of the E-UTRAN through the cell selection procedurefor performing the RRC connection re-establishment procedure, the UEstops the RRC connection re-establishment procedure and enters the RRCidle state (S750).

The UE may be implemented to finish checking whether the selected cellis a suitable cell through the cell selection procedure and thereception of the system information of the selected cell. To this end,the UE may drive a timer when the RRC connection re-establishmentprocedure is started. The timer may be stopped if it is determined thatthe UE has selected a suitable cell. If the timer expires, the UE mayconsider that the RRC connection re-establishment procedure has failed,and may enter the RRC idle state. Such a timer is hereinafter called anRLF timer. In LTE spec TS 36.331, a timer named “T311” may be used as anRLF timer. The UE may obtain the set value of the timer from the systeminformation of the serving cell.

If an RRC connection re-establishment request message is received fromthe UE and the request is accepted, a cell sends an RRC connectionre-establishment message to the UE.

The UE that has received the RRC connection re-establishment messagefrom the cell reconfigures a PDCP sublayer and an RLC sublayer with anSRB1. Furthermore, the UE calculates various key values related tosecurity setting, and reconfigures a PDCP sublayer responsible forsecurity as the newly calculated security key values. Accordingly, theSRB 1 between the UE and the cell is open, and the UE and the cell mayexchange RRC control messages. The UE completes the restart of the SRB1,and sends an RRC connection re-establishment complete message indicativeof that the RRC connection re-establishment procedure has been completedto the cell (S760).

In contrast, if the RRC connection re-establishment request message isreceived from the UE and the request is not accepted, the cell sends anRRC connection re-establishment reject message to the UE.

If the RRC connection re-establishment procedure is successfullyperformed, the cell and the UE perform an RRC connection reconfigurationprocedure. Accordingly, the UE recovers the state prior to the executionof the RRC connection re-establishment procedure, and the continuity ofservice is guaranteed to the upmost.

Hereinafter, an MBMS and a multicast/broadcast single frequency network(MBSFN) are described.

MBSFN transmission or MBSFN-mode transmission refers to a simultaneoustransmission scheme in which a plurality of cells transmits the samesignal at the same time. MBSFN transmissions from a plurality of cellswithin an MBSFN area are perceived as a single transmission for a UE.

The MBMS service may be managed or localized in a cell-based orgeography-based manner. An area in which a specific MBMS service isprovided is widely referred to as an MBMS service area. For example, ifan area in which a specific MBSMS service A proceeds is an MBMS servicearea A, a network in the MBMS service area A may be in a state oftransmitting the MBMS service A. In this case, the UE may receive theMBMS service A according to a UE capability. The MBMS service area maybe defined in terms of an application and a service as to whether aspecific service is provided in a specific area.

A transport channel for the MBMS, that is, a multicast channel (MCH),may be mapped to a logical channel, e.g., a multicast control channel(MCCH) or a multicast traffic channel (MTCH). The MCCH transmits anMBMS-related RRC message, and the MTCH transmits a traffic of a specificMBMS service. One MCCH exists in every one MBMS single frequency network(MBSFN) region for transmitting the same MBMS information/traffic. TheMCCH includes one MBSFN region configuration RRC message, and has a listof all MBMS services. If the MBMS-related RRC message is changed in aspecific MCCH, a physical downlink control channel (PDCCH) transmits anMBMS radio network temporary identity (M-RNTI) and an indication forindicating the specific MCCH. The UE which supports the MBMS may receivethe M-RNTI and the MCCH indication through the PDCCH, may recognize thatthe MBMS-related RRC message is changed in the specific MCCH, and mayreceive the specific MCCH. The RRC message of the MCCH may be changed inevery modification period, and is broadcast repetitively in everyrepetition period. A notification mechanism is used to inform an MCCHchange caused by a presence of an MCCH session start or MBMS countingrequest message. The UE detects the MCCH change informed without havingto depend on the notification mechanism through MCCH monitoring in themodification period. The MTCH is a logical channel on which an MBMSservice carried. If many services are provided in an MBSFN region, aplurality of MTCHs may be configured.

A UE may also be provided with a dedicated service while being providedwith an MBMS service. For example, a user may chat on the user's ownsmartphone using an instant messaging (IM) service, such as MSN orSkype, simultaneously with watching a TV on the smartphone through anMBMS service. In this case, the MBMS service is provided through an MTCHreceived by a plurality of UEs at the same time, while a serviceprovided for each individual UE, such as the IM service, is providedthrough a dedicated bearer, such as a dedicated control channel (DCCH)or dedicated traffic channel (DTCH).

In one area, a BS may use a plurality of frequencies at the same time.In this case, in order to efficiently use radio resources, a network mayselect one of the frequencies to provide an MBMS service only in thefrequency and may provide a dedicated bearer for each UE in allfrequencies. In this case, when a UE, which has been provided with aservice using a dedicated bearer in a frequency where no MBMS service isprovided, wishes to be provided with an MBMS service, the UE needs to behanded over to an MBMS providing frequency. To this end, the UEtransmits an MBMS interest indication to a BS. That is, when the UEwishes to receive an MBMS service, the UE transmits an MBMS interestindication to the BS. When the BS receives the indication, the BSrecognizes that the UE wishes to receive the MBMS service and hands theUE over to an MBMS providing frequency. Here, the MBMS interestindication is information indicating that the UE wishes to receive anMBMS service, which additionally includes information on a frequency towhich the UE wishes to be handed over.

The UE, which wishes to receive a specific MBMS service, firstidentifies information on a frequency at which the specific service isprovided and information on broadcast time at which the specific serviceis provided. When the MBMS service is already on air or is about to beon air, the UE assigns a highest priority to the frequency at which theMBMS service is provided. The UE performs a cell reselection procedureusing reset frequency priority information and moves to a cell providingthe MBMS service to receive the MBMS service.

When the UE is receiving an MBMS service or is interested in receivingan MBMS service and when the UE is allowed to receive an MBMS servicewhile camping on an MBMS service-providing frequency, it may beconsidered that the frequency is assigned a highest priority during anMBMS session as long as the following situations last while thereselected cell is broadcasting SIB13.

-   -   When SIB15 of a serving cell indicates that one or more MBMS        service area identities (SAIs) are included in the user service        description (USD) of the service.    -   SIB15 is not broadcast in a serving cell, and the frequency is        included in the USD of the service.

A UE needs to be able to receive an MBMS in RRC_IDLE and RRC_CONNECTEDstates.

In the RRC_IDLE state, the UE may operate as follows. 1) UE-specific DRXmay be set by an upper layer. 2) The UE monitors a paging channel todetect a call, a system information change, and an ETWS notification andperforms adjacent cell measurement and cell selection (reselection). TheUE may acquire system information and may perform possible measurement.

In the RRC_CONNECTED state, the UE may transmit unicast data and may setUE-specific DRX in a lower layer. The UE supporting CA may use one ormore secondary cells along with a primary cell.

The UE monitors the paging channel and monitors the content of systeminformation block (SIB) type 1 to detect a system information change. Todetermine whether data is scheduled for the UE, the UE monitors controlchannels associated with a shared data channel. Further, the UE provideschannel quality and feedback information. The UE may measure aneighboring cell, may report a measurement result, and acquires systeminformation.

FIG. 8 shows a structure of an MBSFN subframe.

Referring to FIG. 8, MBSFN transmission is configured by the subframe. Asubframe configured to perform MBSFN transmission is referred to as anMBSFN subframe. In a subframe configured as an MBSFN subframe, MBSFNtransmission is performed in OFDM symbols other than first two OFDMsymbols for PDCH transmission. For convenience, a region used for MBSFNtransmission is defined as an MBSFN region. In the MBSFN region, no CRSfor unicast is transmitted but an MBMS-dedicated RS common to all cellsparticipating in transmission is used.

In order to notify even a UE receiving no MBMS that no CRS istransmitted in the MBSFN region, system information on a cell isbroadcast including configuration information on the MBSSFN subframe.Since most UEs perform radio resource management (RRM), radio linkfailure (RLF) processing, and synchronization using a CRS, it isimportant to indicate the absence of a CRS in a specific region. A CRSis transmitted in first two OFDM symbols used as a PDCCH in the MBSFNsubframe, and this CRS is not for an MBSFN. A CP of the CRS transmittedin the first two OFDM symbols used as the PDCCH in the MBSFN subframe(that is, whether the CRS uses a normal CP or an extended CP) follows aCP applied to a normal subframe, that is, a subframe which is not anMBSFN subframe. For example, when a normal subframe 811 uses a normalCP, a CRS according to the normal CP is also used in the first two OFDMsymbols 812 of the MBSFN subframe.

Meanwhile, a subframe to be configured as an MBSFN subframe isdesignated by FDD and TDD, and a bitmap is used to indicate whether asubframe is an MBSFN subframe. That is, when a bit corresponding to aspecific subframe in a bitmap is 1, it is indicated that the specificsubframe is configured as an MBSFN subframe.

FIG. 9 shows an example of an MBSFN subframe configuration forperforming an MBMS service.

Referring to FIG. 9, a UE acquires MBSFN subframe configurationinformation, MBSFN notification configuration information, and MBSFNarea information list to perform the MBMS service.

The UE may know the MBSFN subframe configuration information, that is, aposition of an MBSFN subframe, through SIB2 and RRC dedicated signaling.For example, the MBSFN subframe configuration information may beincluded in an MBSFN-SubframeConfig information element (IE).

In addition, the UE may acquire the MBSFN area information list and theMBMS notification configuration information as information required toacquire MBMS control information related to one or more MBSFN regions inwhich the MBMS service can be performed through SIB13. Herein, for eachMBSFN region, the MBSFN area information list may include an MBSFNregion ID, information regarding an MBSFN region in an MBSFN subframe ina corresponding MBSFN region, information such as an MBSFN subframeposition at which transmission of an MCCH occurs as an MBMS controlinformation channel, or the like. For example, the MBSFN areainformation list may be included in an MBSFN-AreaInfoList informationelement. Meanwhile, the MBSFN notification configuration information isconfiguration information for a subframe position at which an MBMSnotification occurs to inform that there is a change in the MBSFN regionconfiguration information. For example, the MBSFN notificationconfiguration information may be included in an MBMS-NotificationConfiginformation element. The MBSFN notification configuration informationincludes time information utilized to notify an MCCH change applicableto all MBSFN regions. For example, the time information may include anotification repetition coefficient (notificationRepetitionCoeff), anotification offset (notificationOffset), and a notification subframeindex (notificationSF-Index). Herein, the notification repetitioncoefficient implies a common notification repetition period for allMCCHs. The notification offset indicates an offset of a radio frame inwhich the MCCH change notification information is scheduled. Inaddition, the notification subframe index is a subframe index used totransmit an MCCH change notification on a PDCCH.

The UE may acquire the MBSFN region configuration information through anMCCH corresponding to each of the MBSFN regions acquired through SIB13.The MBSFN region configuration information may be included in anMBSFNAreaconfiguration message, and contains information regardingphysical multicast channels (PMCHs) used in a corresponding MBSFNregion. For example, information regarding each PMCH may include aposition of an MBSFN subframe in which a corresponding PMCH is located,modulation and coding scheme (MCS) level information used for datatransmission in a corresponding subframe, MBMS service informationtransmitted by the corresponding PMCH, or the like.

The UE receives MCH data through the MTCH on the basis of the PMCH.Scheduling on a time for the MCH data may be known through MCHscheduling information (MSI) delivered through the PMCH. The MSIcontains information regarding how long corresponding MCH datatransmission is continued.

Hereinafter, single-cell point-to-multipoint (SCPTM) transmission isdescribed.

A transmission method of an MBMS service includes SCPTM transmission andmultimedia broadcast multicast service single frequency network (MBSFN)transmission. While identifiable signals are transmitted simultaneouslyin a plurality of cells in the MBSFN transmission, the MBMS service istransmitted in a single cell in the SCPTM transmission. Therefore,unlike in the MBSFN transmission, synchronization between cells is notnecessary in the SCPTM transmission. Further, the SCPTM transmissiondirectly uses the existing PDSCH, and thus has a unicast feature unlikein the MBSFN transmission. That is, a plurality of UEs read the samePDCCH, and acquire an RNTI for each service to receive an SCPTM service.An SCPTM-dedicated MCCH is introduced, and if it is determined that aservice desired by the UE is an SCPTM service through the MCCH, the UEmay acquire a corresponding RNTI value and read a PDCCH through acorresponding RNTI to receive the SCPTM service.

In a current eMBMS structure, during the UE is in an RRC_CONNECTED mode,the UE may inform a serving cell about a carrier frequency at which aninteresting MBMS service is scheduled to support service continuity.Then, there is a high probability that an eNB allows the UE to move to acell on a carrier frequency for carrying the MBMS service. However, thefollowing problem may occur when the aforementioned method is applied toSCPTM transmission to support the service continuity.

FIG. 10 shows a problem for supporting service continuity.

Referring to FIG. 10, it is assumed that a UE is currently in anRRC_CONNECTED state, and receives a first group call service throughSCPTM of a cell 2. It is also assumed that, during the UE receives thefirst group call service through the SCPTM of the cell 2, the UE movesto an overlapping region of a cell 6 and a cell 7. However, since afirst eNB does not know about the cell 6 of a second eNB for providing asecond group call service and the cell 7 of a third eNB for providingthe first group call service, the first group call service may beinterrupted when the first eNB performs handover to the cell 6 of thesecond eNB for providing the second group call service. The presentinvention proposes a method for solving this problem.

FIG. 11 shows a method in which an eNB supporting an SCPTM serviceprovides identification information to a neighboring eNB according to anembodiment of the present invention. The eNB and the neighboring eNB mayhave an X2 connectivity.

Referring to FIG. 11, a first eNB may transmit an X2 setup requestmessage including per-cell information of the first eNB to a second eNB(S1110). The per-cell information of the first eNB may be information(e.g., a temporary mobile group identifier (TMGI)) capable ofidentifying a group call service which is being provided by a cell ofthe first eNB.

The second eNB may transmit an X2 setup response message includingper-cell information of the second eNB to the first eNB (S1120). Theper-cell information of the second eNB may be information (e.g., atemporary mobile group identifier (TMGI)) capable of identifying a groupcall service which is being provided by a cell of the second eNB.

After an X2 setup procedure, if a UE which has received a group callservice through an SCPTM operation is handed over from the first eNB tothe second eNB, a target cell of the UE may be determined by the firsteNB according to information regarding a group call service provided bythe second eNB and received by the first eNB.

FIG. 12 shows a method in which an eNB supporting an SCPTM serviceprovides identification information to a neighboring eNB according to anembodiment of the present invention. The eNB and the neighboring eNB mayhave an X2 connectivity. A method in which an eNB subjected to a changein an SCPTM operation informs a neighboring eNB about a changedconfiguration is proposed when there is a change in an SCPTM operationfor one or more cells.

Referring to FIG. 12, a first eNB may start, update, or stop an SCPTMoperation for one or more cells of the first eNB (S1210).

The first eNB may inform the second eNB about per-cell updateinformation of the first eNB by using an eNB configuration updatemessage (S1220). The per-cell information of the second eNB may beinformation (e.g., a temporary mobile group identifier (TMGI)) capableof identifying a group call service which is being provided by a cell ofthe first eNB.

Upon receiving the eNB configuration update message from the first eNB,the second eNB may update information received from the first eNB(S1230).

Through the same procedure, the per-cell information of the second eNBmay be transmitted to the first eNB. After the eNB configuration updateprocedure, if a UE which has received the group call service through theSCPTM operation is handed over from the first eNB to the second eNB, atarget cell of the UE may be determined by the first eNB according toinformation regarding a group call service provided by the second eNBand received by the first eNB.

For the method described in FIG. 11 and FIG. 12, TMGI information may beincluded in served cell information. The TMGI may identify only an MBMSbearer service, and may include information of Table 1 below.

TABLE 1 Pres- IE Type and IE/Group Name ence Range Reference DescriptionTMGI >PLMN M 9.2.4 Identification >Service ID M OCTET STRING (SIZE (3))

Although the group call service is described for example to clarify theexplanation in the embodiment of FIG. 11 and FIG. 12, the presentinvention is not limited thereto, and thus may also be applied to othertypes of SCPTM services.

FIG. 13 shows a method in which a multi-cell coordination entity (MCE)provides a cell ID list to an eNB according to an embodiment of thepresent invention. In order for the MCE to instruct an SCTPM service ofneighboring eNBs to the eNB, the MCE may directly provide a cell ID listreceived from a core network (CN).

Referring to FIG. 13, the MCE may receive the cell ID list from an MMEthrough any one of an MBMS session start request message, an MBMSsession update request message, and an MBMS session stop request message(S1310). For example, the MME may transmit to the MCE the MBMS sessionstart request message or MBMS session update request message includingthe cell ID list. The cell ID list may include a maximum value of a cellfor an MBMS service. The maximum value of the cell for the MBMS servicemay be 4096.

The MCE may transmit the cell ID list to the eNB through any one of theMBMS session start request message, MBMS session update request message,or MBMS session stop request message including the cell ID list receivedfrom the MME (S1320). For example, in the SCPTM operation, the MCE mayhave SCPTM information (i.e., the cell ID list received from the MME andQoS information) included in the MBMS session start request message orthe MBMS session update request message. The SCPTM information mayinclude a maximum value of a cell for an MBMS service. The maximum valueof the cell for the MBMS service may be 4096. The maximum value of thecell for the MBMS service included in the cell ID list transmitted bythe MME may be identical to the maximum value of the cell for the MBMSservice included in the SCPTM information transmitted by the MCE. Thatis, the cell ID list transmitted to the eNB may be identical to the cellID list received from the MME. In other words, the MCE may directlydeliver to the eNB the cell ID list received from the MME.

Upon receiving the MBMS session start request message or the MBMSsession update request message, the eNB may identify cells ofneighboring eNBs for providing the same SCPTM service on the basis ofthe cell ID list and TMGI included in the message (S1330). The identicalSCPTM service may be an identical group call service. The eNB may storethe cell ID list and TMGI for each cell belonging to the neighboringeNB, and may use this information to support service continuity. Uponreceiving the MSMB session stop request message, the eNB may remove thecell ID list and TMGI for each cell belonging to the neighboring eNB.

The eNB may transmit to the MCE an MBMS session start response message,an MBMS session update response message, or an MBMS session stopresponse message (S1340).

FIG. 14 is a block diagram illustrating a method in which an MCEtransmits a list of cells for providing an SCPTM service according to anembodiment of the present invention.

Referring to FIG. 14, the MCE may receive a cell ID list from an MME(S1410). The cell ID list received from the MME may include a list ofcells for providing the SCPTM service. The cell for providing the SCPTMservice may be a cell for providing the SCPTM service among cellsmanaged by the MME. The cell ID list received from the MME may bereceived by being included in any one of an MBMS session start requestmessage, an MBSM session update request message, and an MBMS sessionstop request message.

The MCE may transmit to the eNB the cell ID list received from the MME(S1420). The cell ID list transmitted to the eNB may be identical to thecell ID list received from the MME. In other words, the MCE may transmitdirectly (i.e., without alteration) to the eNB the cell ID list receivedfrom the MME. The cell ID list transmitted to the eNB may be transmittedby being included in any one of the MBMS session start request message,the MBMS session update request message, and the MBMS session stoprequest message.

Further, the MCE may receive any one of an MBMS session start responsemessage, an MBMS session update response message, and an MBMS sessionstop response message.

FIG. 15 is a block diagram illustrating a method in which an eNBreceives a list or cells for providing an SCPTM service according to anembodiment of the present invention.

Referring to FIG. 15, the eNB may receive from an MCE a cell ID listreceived from an MME (S1510). The cell ID list received from the MCE maybe identical to the cell ID list received from the MME. In other words,the eNB may receive directly (i.e., without alteration) from the MCE thecell ID list received from the MME. The cell ID list received from theMME may include a list of cells for providing the SCPTM service. Thecell for providing the SCPTM service may be a cell for providing theSCTPM service among cells managed by the MME.

The eNB may perform the SCPTM service on the basis of the cell ID listreceived from the MCE (S1520). The cell ID list received from the MCEmay be received by being included in an MBMS session start requestmessage or an MBSM session update request message. Further, the eNB maystore the cell ID list received from the MCE. The cell ID list receivedfrom the MCE may be received by being included in an MSMS session stoprequest message. Further, the base station may remove the cell ID listreceived from the MCE.

FIG. 16 is a block diagram illustrating a wireless communication systemaccording to the embodiment of the present invention.

A BS 1600 includes a processor 1601, a memory 1602 and a transceiver1603. The memory 1602 is connected to the processor 1601, and storesvarious information for driving the processor 1601. The transceiver 1603is connected to the processor 1601, and transmits and/or receives radiosignals. The processor 1601 implements proposed functions, processesand/or methods. In the above embodiment, an operation of the basestation may be implemented by the processor 1601.

A UE 1610 includes a processor 1611, a memory 1612 and a transceiver1613. The memory 1612 is connected to the processor 1611, and storesvarious information for driving the processor 1611. The transceiver 1613is connected to the processor 1611, and transmits and/or receives radiosignals. The processor 1611 implements proposed functions, processesand/or methods. In the above embodiment, an operation of the UE may beimplemented by the processor 1611.

The processor may include an application-specific integrated circuit(ASIC), a separate chipset, a logic circuit, and/or a data processingunit. The memory may include a read-only memory (ROM), a random accessmemory (RAM), a flash memory, a memory card, a storage medium, and/orother equivalent storage devices. The transceiver may include abase-band circuit for processing a wireless signal. When the embodimentis implemented in software, the aforementioned methods can beimplemented with a module (i.e., process, function, etc.) for performingthe aforementioned functions. The module may be stored in the memory andmay be performed by the processor. The memory may be located inside oroutside the processor, and may be coupled to the processor by usingvarious well-known means.

Various methods based on the present specification have been describedby referring to drawings and reference numerals given in the drawings onthe basis of the aforementioned examples. Although each method describesmultiple steps or blocks in a specific order for convenience ofexplanation, the invention disclosed in the claims is not limited to theorder of the steps or blocks, and each step or block can be implementedin a different order, or can be performed simultaneously with othersteps or blocks. In addition, those ordinarily skilled in the art canknow that the invention is not limited to each of the steps or blocks,and at least one different step can be added or deleted withoutdeparting from the scope and spirit of the invention.

The aforementioned embodiment includes various examples. It should benoted that those ordinarily skilled in the art know that all possiblecombinations of examples cannot be explained, and also know that variouscombinations can be derived from the technique of the presentspecification. Therefore, the protection scope of the invention shouldbe determined by combining various examples described in the detailedexplanation, without departing from the scope of the following claims.

What is claimed is:
 1. A method in which a first entity for multi-cellcoordination transmits a list of cells providing a single-cellpoint-to-multipoint (SCPTM) service in a wireless communication system,the method comprising: receiving a cell identification (ID) listincluding identification of at least one cell, from a second entity formobility management; and transmitting the cell ID list including theidentification of at least one cell, which is received from the secondentity, to a base station, wherein the cell ID list transmitted to thebase station is identical to the cell ID list received from the secondentity.
 2. The method of claim 1, wherein the at least one cell providesthe SCPTM service.
 3. The method of claim 1, wherein the at least onecell providing the SCPTM service is at least one cell providing theSCPTM service among cells managed by the second entity.
 4. The method ofclaim 1, further comprising: receiving at least one of a multimediabroadcast/multicast service (MBMS) session start response message, anMBMS session update response message, or an MBSM session stop responsemessage.
 5. The method of claim 1, wherein the cell ID list receivedfrom the second entity is received by being comprised in at least one ofan MBMS session start request message, an MBMS session update requestmessage or an MBSM session stop request message.
 6. The method of claim1, wherein the cell ID list transmitted to the base station istransmitted by being comprised in at least one of an MBSM session startrequest message, an MBSM session update request message, or an MBMSsession stop request message.
 7. The method of claim 1, wherein the basestation is connected with the second entity via the first entity.
 8. Amethod in which a base station receives a list of cells providing asingle-cell point-to-multipoint (SCPTM) service in a wirelesscommunication system, the method comprising: receiving, from a firstentity for multi-cell coordination, a cell identification (ID) listincluding identification of at least one cell providing the SCPTMservice, wherein the cell ID list had been received by the first entityfrom a second entity for mobility management, wherein the cell ID listreceived from the first entity is identical to the cell ID list receivedfrom the second entity; performing the SCPTM service on at least onecell in the base station, based on the cell ID list received from thefirst entity; and identifying at least one cell providing the SCPTMservice in a neighboring base station, based on the cell ID listreceived from the first entity.
 9. The method of claim 8, wherein the atleast one cell providing the SCPTM service is at least one cellproviding the SCPTM service among cells managed by the second entity.10. The method of claim 8, wherein the cell ID list received from thefirst entity is received by being comprised in at least one of amultimedia broadcast/multicast service (MBMS) session start requestmessage or an MBMS session update request message.
 11. The method ofclaim 10, further comprising: storing, by the base station, the cell IDlist received from the first entity.
 12. The method of claim 8, whereinthe cell ID list received from the first entity is received by beingincluded in an MBMS session stop request message.
 13. The method ofclaim 12, further comprising: removing, by the base station, the cell IDlist received from the first entity.
 14. The method of claim 8, whereinthe base station is connected with the second entity via the firstentity.
 15. A first entity for multi-cell coordination transmitting alist of cells providing a single-cell point-to-multipoint (SCPTM)service in a wireless communication system, the first entity comprising:a memory; a transceiver, and a processor operatively coupled to thememory and the transceiver, wherein the processor is configured for:controlling the transceiver to receive a cell identification (ID) listincluding identification of at least one cell, from a second entity formobility management, controlling the transceiver to transmit the cell IDlist including the identification of at least one cell, which isreceived from the second entity, to a base station, and wherein the cellID list transmitted to the base station is identical to the cell ID listreceived from the second entity.
 16. The first entity of claim 15,wherein the at least one cell provides the SCPTM service.
 17. The firstentity of claim 15, wherein the at least one cell providing the SCPTMservice is at least one cell providing the SCPTM service among cellsmanaged by the second entity.
 18. The first entity of claim 15, whereinthe cell ID list received from the second entity is received by beingcomprised in at least one of an MBMS session start request message, anMBMS session update request message or an MBSM session stop requestmessage.
 19. The first entity of claim 15, wherein the cell ID listtransmitted to the base station is transmitted by being comprised in atleast one of an MBSM session start request message, an MBSM sessionupdate request message, or an MBMS session stop request message.
 20. Thefirst entity of claim 15, wherein the base station is connected with thesecond entity via the first entity.